Mars, the fourth planet from the Sun, is a rocky planet with a thin atmosphere and a diameter about half that of Earth's. The surface of the planet is heavily cratered and also has mountains, valleys, canyons, and polar ice caps that are familiar to us on Earth. Although the current environment of Mars is extremely dry and cold, surface features indicate that liquid water once existed on its surface.
NASA's Curiosity rover, which landed on Mars in 2012, captured images of rocky outcrops of rounded pebbles that were found among alluvial fans—cone-shaped deposits of sediment formed by liquid flowing downhill. The pebbles were likely rounded by transportation through water over a long distance.
| Keyboard Shortcut | Action |
|---|---|
| Space | Pause/Play video playback |
| Enter | Pause/Play video playback |
| m | Mute/Unmute video volume |
| Up and Down arrows | Increase and decrease volume by 10% |
| Right and Left arrows | Seek forward or backward by 5 seconds |
| 0-9 | Fast seek to x% of the video. |
| f | Enter or exit fullscreen. (Note: To exit fullscreen in flash press the Esc key. |
| c | Press c to toggle captions on or off |
Watch this video about the discovery of the Martian streambed.
In the box below, describe how scientists used knowledge about geological processes on Earth to interpret the pebble deposits that were found on Mars. What is the significance of the finding?